Former president Thabo Mbeki has paid a glowing tribute to Sudan president Omar Hassan al-Bashir ahead of the country's secession referendum on Sunday.

Mbeki, speaking at a function at the University of Khartoum on Wednesday, said that Al-Bashir, 67, who was indicted in the International Criminal Court (ICC) for alleged war crimes in Darfur in 2009, had accepted the secession referendum in a graceful, generous and humane manner.

"There is no greater test of statesmanship than to accept, in a graceful, generous and humane manner, the decision of those of your people who have the opportunity to choose secession," said Mbeki, who chaired a committee to investigate human rights violations in Darfur and to mediate between the ICC and Sudan.

"We are very mindful of the sacrifices the political leaders of Sudan have to make, even in terms of their personal lives, to play their roles as change agents for the creation of a new reality which portends a future of hope, happiness and a better life for all the people of Sudan."

Some two-million people died in the two decade civil war fought between Southern Sudan and the government.

Mbeki said in a speech prepared for delivery that the referendum would give Sudan a chance to make a new beginning.

"What we would like to say to you in this regard is that we are convinced that regardless of the outcome of the referendum, you and all of us should value it as a decisive moment which gives Sudan the historic possibility to make a new beginning, a new start towards a future of hope, peace and a better life for all the people of Sudan," he said.

Mbeki said "the concept of the construction of two viable states" meant that the two governments would work together to ensure that each state was economically viable, secure and stable and had territorial integrity.

"The two governments will take all necessary measures to ensure that southerners resident in the North and northerners in the South are not adversely affected by the separation in terms of their socio-economic rights. Among other things this means that nobody will be rendered stateless."

Al-Bashir, who is wanted on allegations of genocide and other atrocities committed in Sudan's western Darfur region, has promised to maintain strong economic ties with the mainly Christian South should its people choose to secede.